In many semiconductor devices, an integrated-circuit chip is mounted on the bottom of a gold-plated cavity of a hermetically sealed package with connecting wire leads extending from the package. Fine aluminum wires are bonded to the wire lead frame and the integrated-circuit chip. Usually, the circuit chip is grounded by means of a metal terminal chip or jumper chip, which is bonded to the gold-coated cavity adjacent the circuit chip by scrubbing and heating. The use of a jumper chip is necessary to avoid the formation of an intermetallic compound between aluminum and gold, known as purple or white plague, which forms when a sealing step is carried out at elevated temperature and weakens the bond. A weakened bond decreases the electrical conductivity which may result in bond failure and decreases the reliability of the semiconductor device. The scrubbing of the gold layer of the cavity with the jumper chip is necessary to provide an adequate bond between the jumper chip and the cavity of the device package.
During a study of the ability of gold silicon alloys to wet substrates, we had observed that when a thin preform of Au--Si alloys was melted, a skin of transparent material formed around the preform. This skin was able to hold the melted alloy within it and was one of the reasons that it is necessary to scrub chips to make Au--Si alloy performs wet and adhere to a substrate.